Estimates of African, European, and Amerindian contributions to the gene pool of 11 predominantly African-derived South American populations were obtained using five autosomal and one Y chromosome hypervariable loci, as well as mitochondrial DNA (sequences of the first hypervariable segment of the control region, plus two restriction sites and the presence or absence of the CoII/tRNA(Lys) intergenic 9-bp deletion). The three latter characteristics are reported here for the first time for 42 individuals living in three Brazilian populations. Thirty-eight sequences were identified in these persons; 17 (45%) could be classified as being of African, 4 (11%) of Amerindian, and 2 (5%) of European origin. Evidence for asymmetrical matings in relation to sex and ethnic group was obtained for nine of the 11 populations. The most consistent finding was the introduction of European genes through males, but the results differ in the several communities, indicating the importance of local factors in such interactions. Am. J. Hum. Biol. 11:551-563, 1999. Copyright 1999 Wiley-Liss, Inc.